Electro-acoustic transducer having vibrating function and method of manufacturing the same

ABSTRACT

A mechanical resonance frequency of a vibration section of an electro-acoustic transducer having a vibrating function is measured during an assembly process, and is compared with a predetermined mechanical resonance frequency. Based on a difference obtained by this comparison, a weight to be attached and a position for fixing a vibration section to a frame is determined. In accordance with this determination, the weight for resonance frequency adjustment is attached to the vibration section, or suspension and the frame which have been provisionally fixed are fixed again. Thus, the predetermined mechanical resonance frequency can be obtained steadily. As a result, an electro-acoustic transducer having a vibrating function with stabilized mechanical resonance frequency of the vibration section can be produced.

This application is a National Stage of PCT/JP02/11062, filed Oct. 24,2002.

TECHNICAL FIELD

The present invention relates to an electro-acoustic transducer having avibrating function, and a method for manufacturing the transducer.

BACKGROUND ART

A conventional electro-acoustic transducer having a vibrating function(hereinafter referred to as a transducer) is disclosed in JapanesePatent Laid-Open Application No. 2000-153231. This conventionaltransducer is described referring to FIGS. 5A and 5B. FIG. 5A is a planview and FIG. 5B is a cross sectional view.

Referring to FIGS. 5A and 5B, the transducer's voice coil 10 a is fixedto a diaphragm 10. A magnetic circuit 11 comprises a magnetic circuitportion 11 a which generates a driving power by flowing an electriccurrent in voice coil 10 a, and a weight portion 11 b which isintegrated with the magnetic circuit portion 11 a. The weight portion 11b is added for a purpose of sensing vibration of vibration section 13,which will be referred to later. If the vibration section 13 generatessufficient vibration, the weight portion 11 b can be omitted.

Magnetic circuit portion 11 a and weight portion 11 b are supported by aframe 16 via a suspension 12. Vibration section 13 comprises magneticcircuit 11 and suspension 12. Diaphragm 10 and voice coil 10 aconstitute a mechanical resonance circuit of an acoustic section.Magnetic circuit 11 and suspension 12 constitute a mechanical resonancecircuit of vibration section 13.

Weight portion 11 b is a molded resin containing tantalum powder, andsuspension 12 and magnetic circuit portion 11 a are integrated with theweight portion 11 b through an insert molding process to provide aone-piece component. A baffle 17 is bonded to a periphery of diaphragm10, and attached to frame 16.

Now, operation of the above-configured electro-acoustic transducerhaving a vibrating function is described below.

As voice coil 10 a is disposed in a magnetic gap A of magnetic circuitportion 11 a, when an AC current is applied, voice coil 10 a generates adriving force. Since a weight of voice coil 10 a is very small relativeto that of magnetic circuit 11, magnetic circuit 11 does not vibrate atmost frequency ranges, while voice coil 10 a alone vibrates. Thus,diaphragm 10 is vibrated by voice coil 10 a to generate sounds at mostfrequency ranges.

Since vibration section 13 is for sensing vibration of a human body, amechanical resonance frequency of vibration section 13 is set at acertain frequency that is lower than that of the acoustic section.Mechanical impedance of vibration section 13 becomes smallest at themechanical resonance frequency. Therefore, even with a small drivingforce, vibration section 13 can generate a vibration large enough to besensed by the human body. Vibration force at this time is determined bya product of vibration section 13's weight (that is a weight of magneticcircuit 11, in an approximation) and acceleration of vibration section13.

In the conventional transducer having a vibration function operating inaccordance with the above-described principle, the mechanical resonancecircuit comes to have a high resonance sharpness Q in order to vibratevibration section 13 which has a large mass. As a result, vibrationsection 13's mechanical resonance frequency disperses largely relativeto resonance frequency signals delivered to voice coil 10 a from outsidefor vibrating vibration section 13. This dispersion leads toproblematical dispersion of vibrating force. Dispersion in mechanicalresonance frequency is caused by weight dispersion of vibration section13, dispersion in material thickness, width, Young's modulus, and thelike of suspension 12, and supporting position dispersion of suspension12 and other factors.

The present invention addresses the above problems and provides anelectro-acoustic transducer having a vibrating function, wherein themechanical resonance frequency of the vibration section can be adjustedat low cost, and dispersion of vibrating force is reduced.

SUMMARY OF THE INVENTION

An electro-acoustic transducer having a vibrating function of thepresent invention comprises a diaphragm, a voice coil fixed to thediaphragm, a magnetic circuit provided with a magnetic gap in which thevoice coil is inserted, and a vibration section provided withsuspensions for connecting the magnetic circuit to a frame. Weight(s)for adjusting a resonance frequency of the vibration section is(are)attached to the vibration section based on a result of a measurementperformed during a course of a production process, or the frame and thesuspensions are connected at a plurality of connecting positions basedon the above result. The weight(s) for adjusting the resonance frequencyin the present invention is(are) attached so that the weight(s) do(does) not cause shift of a center of gravity of the vibration section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan view of a vibration section (before a diaphragm isattached) of a transducer in accordance with an exemplary embodiment ofthe present invention.

FIG. 2 shows a plan view of a vibration section (before a diaphragm isattached) of a transducer in accordance with another exemplaryembodiment.

FIG. 3 is a cross sectional view showing a welding portion of asuspension and a frame.

FIG. 4 is a plan view showing a welding portion of the suspension andthe frame in another exemplary embodiment.

FIG. 5 A is a plan view of a conventional transducer.

FIG. 5 B is a cross sectional view of the conventional transducer.

DESCRRIPTION OF THE PREFERRED EMBODIMENTS

An electro-acoustic transducer having a vibrating function of thepresent invention is described in the following in accordance withexemplary embodiments, referring to FIG. 1–FIG. 4. In the descriptions,those components identical to conventional technologies are representedby using the same reference numerals and their description is omitted.

First Embodiment

FIG. 1 shows a plan view of a vibration section, which is a key part ofan electro-acoustic transducer having a vibrating function in accordancewith an exemplary embodiment of the present invention. A main point ofdifference from conventional technology is that the transducer hasweights for adjusting a resonance frequency attached to a weightportion.

Referring to FIG. 1, a magnetic circuit 11 comprises a magnetic circuitportion 11 a and a weight portion 11 b which does not practicallyfunction as a part of the magnetic circuit. The magnetic circuit 11 anda suspension 12 (hatched) form a vibration section 13.

Fixing portions 15 between frame 16 and suspension 12 are provided atfour places in a symmetrical arrangement. Although in the presentembodiment these are connected by adhesives, other methods such as acaulking, welding, brazing and the like may be employed. Suspension 12and magnetic circuit portion 11 a are formed integrally when weightportion 11 b is formed by molding resin.

Weight portion 11 b is provided with weights 14 for adjusting amechanical resonance frequency at two places in order to adjustmechanical resonance frequency of vibration section 13. Weights 14 arealigned on a diagonal line passing through a center of gravity ofmagnetic circuit portion 11 a and weight portion 11 b. Therefore, thecenter of gravity after weights 14 are attached does not shift in aplanar direction, and remains at the same position.

Positional arrangement(s) for weight(s) 14 is(are) not necessarily asdescribed above, and a number of the weights may be one or the numbermay be more than one so long as the weight(s) do (does) not shift thecenter of gravity.

If the center of gravity shifts as a result of the positions ofweight(s) 14, vibration section 13 is liable to cause a rolling motionwhen it vibrates.

Now, a process of manufacturing the transducer is described.

Initially, magnetic circuit 11 is fixed to frame 16 via suspension 12 toform vibration section 13. Then, voice coil 10 a attached to dummydiaphragm 10, for example, is inserted into a magnetic gap of magneticcircuit portion 11 a, and a dummy current is applied to voice coil 10 a.Or, a mechanical resonance circuit of vibration section is vibrated byan external source. Through one of these operations, vibration section13's mechanical resonance frequency is measured. Mechanical resonancefrequency f₀ is calculated by the formula below:f ₀=½π√{square root over (mc)}  (Formula 1)

Mass (weight) m of the vibration section is measured previously, andthen using Formula 1, a value of weight 14 that should be attached tothe vibration section for satisfying a predetermined resonance frequencycan be calculated. This weight value is divided by a number of weightpositions (two, in the present embodiment). Weights having this valueare attached at respective positions by using adhesive or the like.

Then, real diaphragm 10 with voice coil 10 a is attached to frame 16with the voice coil 10 a inserted into a magnetic gap of magneticcircuit 11. A transducer is thus produced.

The above-described manufacturing process can be performed on anassembly line, which can further be automated. Thus, the presentinvention enables highly efficient and stable production of transducershaving a vibrating function, with vibration section 13 having apredetermined resonance frequency.

In the present embodiment, the mechanical resonance frequency ofvibration section 13 is adjusted by adding weights 14. Therefore, aweight of vibration section 13 before attaching weights 14 has to be setto be slightly lighter than designed. This means that the mechanicalresonance frequency is higher than a predetermined frequency. By sodoing, the mechanical resonance frequency can be adjusted rather easilyduring an assembly process to be maintained within an allowable range ofa predetermined mechanical resonance frequency.

In the present embodiment, descriptions are based on a case where aninitial mechanical resonance frequency is measured in the course ofassembling the transducer, and then weights 14 for adjustment areattached in accordance with this measured mechanical resonancefrequency. Besides the above-described way of adjusting, there can be analternative procedure. That is, weights 14 for adjustment can beattached through an opening provided in frame 16 at a placecorresponding to a reverse side of weight portion 11 b. With thisprocedure, resonance frequency adjustment can be made even after atransducer is finished, without using a dummy diaphragm. A furtherimprovement of productivity can also be expected with this procedure.

Second Embodiment

FIG. 2 is a plan view of a vibration section of a transducer in a secondexemplary embodiment. FIG. 3 is a cross sectional view of a weldedportion of the vibration section. FIG. 4 is a plan view showing a weldedportion of a vibration section of a modified exemplary embodiment.

Only a point of difference from the conventional technology is describedwith reference to FIG. 2. Suspension 12 and frame 16 in the presentembodiment are connected by welding. Furthermore, regions 12 a forwelding are provided at four places each having a long length along acircumferential direction of suspension 12 around magnetic circuit 11.

Like in the first embodiment, a mechanical resonance circuit ofvibration section 13 is completed, which is a half-finished stage beforediaphragm 10 is attached. So, mechanic a1 resonance frequency can bemeasured. Therefore, the same procedure can be performed as with thefirst embodiment. Namely, a process for obtaining a predeterminedmechanical resonance frequency is performed based on a differencebetween a mechanical resonance frequency measured by attaching dummydiaphragm 10 to voice coil 10 a and a predetermined mechanical resonancefrequency. In the present embodiment, welding positions betweensuspension 12 and frame 16 are calculated for obtaining thepredetermined mechanical resonance frequency. In practice, suspension 12and frame 16 are provisionally fixed together by welding, and then thesemembers are welded again at a position obtained by the calculation tochange an effective length of suspension 12 supporting the vibrationsection 13. The predetermined mechanical resonance frequency is thusobtained.

Since the mechanical resonance frequency is adjusted to thepredetermined value by adding a welding place between suspension 12 andframe 16, a provisional welding position should be determined so that amechanical resonance frequency is lower than the predetermined value.Described practically, provisional welding should be performed to leavea longer support for suspension 12, and then welding is performed againat a precise point after the mechanical resonance frequency is measuredto obtain the predetermined mechanical resonance frequency. By so doing,the mechanical resonance frequency can be adjusted rather easily duringan assembly process to be maintained within an allowable range of thepredetermined mechanical resonance frequency.

In the above description, suspension 12 and frame 16 are finally weldedat a stage where vibration section 13 is completed, but it is a stagestill half-finished as a transducer. Besides the above-described way ofadjusting, there can be an alternative procedure. That is, a finalwelding of suspension 12 and frame 16 can be performed through anopening provided in frame 16. With this procedure, the resonancefrequency can be adjusted to the predetermined mechanical resonancefrequency even after diaphragm 10 is attached and a appearance of thetransducer is finished. With this procedure, operations of attaching anddetaching a dummy diaphragm is eliminated, and improved productivity canbe expected during production.

FIG. 4 shows a modified example of the present embodiment. Though,suspension 12 in the present embodiment extends in the circumferentialdirection to form a region 12 a for welding, in the modified example thesuspension is expanded also in a radial direction to widen region 12 bfor welding.

In a case where a welding position for obtaining a predeterminedmechanical resonance frequency is very close to an initial weldingposition, the region 12 b for welding which has been expanded also inthe width direction provides a stable welding condition. For example,for a transducer of 20 mm square whose mechanical resonance frequency isapproximately 120 Hz, a subtle adjustment of about 0.2–0.4 mm forshifting the resonance frequency by 2 Hz is required. A welding for suchan adjustment might overlap on the provisional welding. The greaterwidth of region 12 b for welding wider than other part of the suspensionmakes small influence to a compliance of the whole suspension 12. Thisallows to set a large shift amount for the welding position. Thus, theconfiguration is effective to avoid overlapped welding.

The above descriptions have been based on a structure where suspension12 is integrated with weight portion 11 b by molding a resin to form asingle component, and welding is performed only between frame 16 andsuspension 12. However, the present invention is not limited to theabove-described configuration. The weight portion 11 b may be made of ametal such as iron that can be welded so that it can be welded tosuspension 12. In this case, adjustment to the predetermined mechanicalresonance frequency can be conducted between suspension 12 and weightportion 11 b. However, it may be easier and more efficient to conduct awelding operation between frame 16 and suspension 12 with respect toproductivity.

The foregoing descriptions of respective embodiments have been based ona procedure, where a mechanical resonance frequency of an individualvibration section of a transducer is measured after it is attached to aframe, and a difference from a predetermined mechanical resonancefrequency is used for obtaining the predetermined mechanical resonancefrequency. However, when magnetic circuits, suspensions and frames areavailable in a very steady condition, unitized vibration sectionsintegrated with a magnetic circuit, weight portion and suspension can besupplied. In this case, at least one out of one lot of the suppliedvibration section(s) is (are) sampled, and this sample is attached to aframe in the same manner as in the above embodiments to determine aweight for resonance frequency adjustment, or a locational shift forwelding. And, production of electro-acoustic transducers having avibrating function may be performed in accordance with determinationsmade in the above-described sampling process until a new variationfactor arises.

Thus, an individual measurement for each transducer conducted in aprocess of production of an electro-acoustic transducer having avibrating function for a purpose of obtaining a predetermined mechanicalresonance frequency, determination of a weight for resonance frequencyadjustment and determination of a welding position can be eliminated.This contributes to a substantial improvement of productivity.

Namely, in a state where supply conditions influential to a variation ofresonance frequency, such as a suspension material thickness, weight ofa magnetic circuit portion or the like are very stable, excludingtypical lot-to-lot variations, the above-described production processutilizing the sampling measurement leads to a more efficient production.

INDUSTRIAL APPLICABILITY

In production of electro-acoustic transducers having a vibratingfunction, mechanical resonance frequency of the vibrating section can bestabilized in an efficient manner in accordance with the presentinvention. Thus, the present invention provides stable qualityelectro-acoustic transducers having a vibrating function at a low cost,and provides a great influence in industry.

1. A method of manufacturing an electro-acoustic transducer having avibrating function, comprising: providing a vibration section includinga magnetic circuit having a magnetic gap; provisionally fixing saidvibration section to a frame; fixing a diaphragm, having a voice coil,to said frame while said voice coil is positioned within said magneticgap; determining a final fixing position of said vibration sectionrelative to said frame by measuring a mechanical resonance frequency ofsaid vibration section; and welding said vibration section to said framebased on the determined final fixing position.
 2. The method accordingto claim 1, further comprising: finishing an appearance of theelectro-acoustic transducer prior to welding said vibration section tosaid frame.
 3. The method according to claim 1, wherein provisionallyfixing said vibration section to a frame comprises provisionally fixingsaid vibration section to said frame at a position such that amechanical resonance frequency of said vibration section is lower than apredetermined mechanical resonance frequency of said vibration section.4. The method according to claim 1, further comprising: determiningpositions at which said vibration section is to be welded to said frameby determining positions at which said frame would be welded to avibration section, sampled from a production lot of vibration sections,so as to obtain a desired resonance frequency, such that welding saidvibration section to said frame comprises welding said vibration sectionto said frame at said positions.
 5. The method according to claim 4,wherein said vibration section further has a magnetic circuit portionand a suspension, with said magnetic gap being in said magnetic circuitportion, and such that welding said vibration section to said framecomprises welding said suspension to said frame.